Book Image

Scala Functional Programming Patterns

By : Atul S. Khot
Book Image

Scala Functional Programming Patterns

By: Atul S. Khot

Overview of this book

Scala is used to construct elegant class hierarchies for maximum code reuse and extensibility and to implement their behavior using higher-order functions. Its functional programming (FP) features are a boon to help you design “easy to reason about” systems to control the growing software complexities. Knowing how and where to apply the many Scala techniques is challenging. Looking at Scala best practices in the context of what you already know helps you grasp these concepts quickly, and helps you see where and why to use them. This book begins with the rationale behind patterns to help you understand where and why each pattern is applied. You will discover what tail recursion brings to your table and will get an understanding of how to create solutions without mutations. We then explain the concept of memorization and infinite sequences for on-demand computation. Further, the book takes you through Scala’s stackable traits and dependency injection, a popular technique to produce loosely-coupled software systems. You will also explore how to currying favors to your code and how to simplify it by de-construction via pattern matching. We also show you how to do pipeline transformations using higher order functions such as the pipes and filters pattern. Then we guide you through the increasing importance of concurrent programming and the pitfalls of traditional code concurrency. Lastly, the book takes a paradigm shift to show you the different techniques that functional programming brings to your plate. This book is an invaluable source to help you understand and perform functional programming and solve common programming problems using Scala’s programming patterns.
Table of Contents (19 chapters)
Scala Functional Programming Patterns
About the Author
About the Reviewers

Threads – masters and slaves

One more concept at play here is of masters and slaves (also known as workers). The master spawns off a bunch of workers that are connected via a queue.

Then, a worker thread recurs in the directory. Once it finds a file with a .txt extension, it hands over the file to the egrep worker thread, as shown in the following figure. The egrep worker searches for the pattern in the file and prints out the matching lines:

Figure 10.3: Master/slave threads

The master thread recursively traverses the directory, looking for files with the .txt extension. Here is an example of the Java code. We've used the excellent Apache commons io library for the file operations.

Here is how the Java code looks:

public class FilesFinder extends DirectoryWalker 
  implements Runnable { // 1

  private final String directory;
  private final BlockingQueue<File> inputQueue; // 2

  public FilesFinder(final String directory, final BlockingQueue<File> inputQueue) {